An update: I received a PM from Missy asking for the info to cancel the membership. So assuming this is taken care of, I consider the matter resolved.
Insidous, I appreciate your response. Indeed, I did try to look up my original email receipt. In this case, however, the receipt only offers payment information, membership level, and my billing address. It does not include any information on how to cancel or even the name of the company handling the memberships.
Along the same lines, most of the sites that I have joined, including Tickle Abuse and Tickling-Submission, at least offer a link to the website of the company that handles the memberships. From there you can can cancel the membership by providing the information as you have noted. The link is usually small and subtle, but it is generally there nonetheless, and if they don't have one, they at least have information on who to contact to cancel.